This invention relates to speed control systems, and, while the invention is subject to a wide range of applications, a preferred embodiment of the invention will be particularly described as applied to a speed control system for a vehicle.
In speed control systems for governing a vehicle, a turbine, and the like, speed regulation is accomplished by comparing a desired speed signal with a feedback signal characteristic of actual speed. The actual speed signal can be generated as an alternating current signal by an axle driven generator, for example, wherein the frequency of the signal is related to actual speed. Various systems have been disclosed for checking the integrity of the alternating current actual speed signal to ensure safety in a speed governor system, such as the system disclosed in the Wilcox U.S. Pat. No. 3,482,090, which is assigned to the same assignee as the present invention. According to this patent, the frequency of the actual speed signal is compared with a desired frequency setting of a frequency detector to determine a speed limit at which the vehicle can be operated. Integrity of the actual speed signal sensing means in this patent is provided by a checking oscillator organization that checks the circuitry and the cutoff range of the frequency detector. The integrity checking is to insure continuity of axle driven generator circuits for generating a pulse rate indicative of the actual speed of the vehicle. This system is sufficient for vehicles operating under normal headway, but conditions may be encountered where faster response is required, for example, for vehicle operating under closer headway at higher speed.
An object of the present invention is to provide an improved speed governor system which substantially obviates one or more of the limitations and disadvantages of the described prior art systems.
Another object of the present invention is to simplify speed governor systems by eliminating the need for frequency detectors and checking oscillators such as have been required according to the prior art.
Another object of the present invention is to provide an actual speed signal checking system that senses quickly an abnormal actual speed signal.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.